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Distinct roles for STAT1, STAT3, and STAT5 in differentiation gene induction and apoptosis inhibition by
J B Demoulin1, E Van Roost, M Stevens
1Ludwig Institute for Cancer Research and the Experimental Medicine Unit, Université Catholique de Louvain, avenue Hippocrate, 74, B-1200 Brussels, Belgium.
Abstract:
Interleukin-9 (IL-9) activates three distinct STAT proteins: STAT1, STAT3, and STAT5. This process depends on one tyrosine of the IL-9 receptor, which is necessary for proliferation, gene induction, and inhibition of apoptosis induced by glucocorticoids. By introduction of point mutations in amino acids surrounding this tyrosine, we obtained receptors that activated either STAT5 alone or both STAT1 and STAT3, thus providing us with the possibility to study the respective roles of these factors in the biological activities of IL-9. Both mutant receptors were able to prevent apoptosis, but only the mutant that activated STAT1 and STAT3 was able to support induction of granzyme A and L-selectin. In line with these results, constitutively activated STAT5 blocked glucocorticoid-induced apoptosis. In Ba/F3 cells, significant proliferation and pim-1 induction were observed with both STAT-restricted mutants, though proliferation was lower than with the wild-type receptor. These results suggest that survival and cell growth are redundantly controlled by multiple STAT factors, whereas differentiation gene induction is more specifically correlated with individual STAT activation by IL-9.
Insights
Interleukin-9 (IL-9) signaling involves STAT proteins. Mutating the IL-9 receptor revealed STAT5 controls survival, while STAT1/STAT3 mediate differentiation gene induction, impacting cell survival and growth.
Area of Science:
- Immunology
- Molecular Biology
- Cell Signaling
Background:
- Interleukin-9 (IL-9) is a cytokine with diverse cellular functions.
- IL-9 signaling is mediated through the IL-9 receptor, activating Signal Transducer and Activator of Transcription (STAT) proteins.
- Understanding the specific roles of activated STAT proteins is crucial for elucidating IL-9's biological effects.
Purpose of the Study:
- To investigate the distinct roles of STAT1, STAT3, and STAT5 in mediating Interleukin-9 (IL-9) biological activities.
- To dissect the signaling pathways downstream of the IL-9 receptor by creating mutants that selectively activate specific STAT proteins.
- To determine the contribution of individual STAT proteins to IL-9-induced proliferation, gene expression, and apoptosis inhibition.
Main Methods:
- Site-directed mutagenesis of the IL-9 receptor to generate variants activating specific STAT proteins (STAT5 alone, or STAT1 and STAT3).
- Utilizing Ba/F3 cell lines expressing wild-type and mutant IL-9 receptors.
- Assessing apoptosis inhibition, gene induction (granzyme A, L-selectin, pim-1), and cell proliferation in response to IL-9 stimulation.
Main Results:
- Both STAT5-activating and STAT1/STAT3-activating mutants inhibited glucocorticoid-induced apoptosis, suggesting redundant roles in cell survival.
- Only the STAT1/STAT3-activating mutant supported the induction of differentiation markers granzyme A and L-selectin.
- Constitutively active STAT5 blocked glucocorticoid-induced apoptosis, reinforcing its role in cell survival.
- Both mutants induced proliferation and pim-1, but proliferation was lower compared to the wild-type receptor.
Conclusions:
- Cell survival and growth downstream of IL-9 signaling are redundantly regulated by multiple STAT factors.
- Differentiation-associated gene induction by IL-9 is more specifically linked to the activation of individual STAT proteins, particularly STAT1 and STAT3.
- This study provides insights into the differential roles of STAT proteins in mediating the pleiotropic effects of IL-9.